In a field-effect transistor using a fin structure for a channel (hereinafter, “FinFET”), a technique of applying stress to the channel has been known as a method of improving carrier mobility in the channel. For example, in Japanese Patent Application Laid-open No. 2006-351975, an insulating film covers between fins laid out in parallel and the upper part of the fins, to apply compressive stress to a direction perpendicular to a height direction of the fins, thereby improving current driving force, by utilizing a phenomenon that an insulating film works in a direction to contract. In International publication WO 2004/090992, a gate electrode is formed on an upper surface and on a side surface of fins made of silicon, and an interlayer film having a linear expansion coefficient smaller than that of silicon is formed on this gate electrode. With this arrangement, tensile strain is applied to a direction perpendicular to a height direction of the fins, thereby improving mobility. As explained above, according to the techniques of Japanese Patent Application Laid-open No. 2006-351975 and WO2004/090992, an insulating film is formed on a side surface and on an upper surface of fins on which a gate electrode is laid out, thereby applying stress to mainly a direction perpendicular to a height direction of the fins.
According to the FinFET, when more stress is applied to a channel region of the fins, carrier mobility of the channel is improved more. Therefore, there has been desired a technique capable of applying more stress to the fins of the FinFET in the structure shown in techniques of Japanese Patent Application Laid-open No. 2006-351975 and WO2004/090992. It has been conventionally known that, in the FinFET, when stress is applied to a height direction of the fins, carrier mobility can be improved most effectively in the channel (for example, see Kyoung sub Shin, et al., “Dual Stress Capping Layer Enhancement Study for Hybrid Orientation FinFET CMOS Technology”, 2005 IEEE). However, in the techniques of Japanese Patent Application Laid-open No. 2006-351975 and WO2004/090992, because stress is applied to a direction perpendicular to the height direction of the fins, this has not been effective to improve carrier mobility in the channel of the FinFET.